overvoltage
/ˈəʊvəˌvəʊltɪdʒ/ /ˈəʊvəˌvɒltɪdʒ/noun
1 Chemistry. The extra potential above the value for theoretical, reversible conditions which must be applied to an electrolytic cell to liberate a substance at an electrode in practical, irreversible conditions.
2A voltage in excess of some threshold value, or of that which is normal, safe, or allowed for.
Origin
Early 20th century. From over- + voltage. Compare German Überspannung.